Pacific Science Volume 51, Number 4, 1997
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Pacific Science is a quarterly publication devoted to the biological and physical sciences of the Pacific Region.
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Item51: Index - Pacific Science(University of Hawaii Press, 1997)
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ItemComparisons to the Century Before: The Legacy of R. C. L. Perkins and Fauna Hawaiiensis as the Basis for a Long-Term Ecological Monitoring Program(University of Hawaii Press, 1997-10)As one means of assessing the impact of the past 100 yr of development and biological alteration in Hawai'i, the damselfly (Odonata: Coenagrionidae) and carabid beetle (Coleoptera: Carabidae) collections of R. C. L. Perkins made in the l890s are compared with similar collections made one century later during the 1990s. Two islands that have experienced very different histories of development are compared: O'ahu and Moloka'i. Of eight native damselfly species originally inhabiting O'ahu, one has been extirpated from the island, another is now reduced to a single population, and three more are at risk. Of the eight species originally found on Moloka'i, by contrast, there is only one species that has not been rediscovered, although there is reasonable probability that it has simply eluded capture because of inherent rarity, whereas the remaining species retain large and stable populations. Capture frequencies (based on specimens collected per decade) are lower now than in the preceding century for most species on O'ahu, even allowing for modem collectors retaining fewer specimens. The only species on O'ahu for which captures have increased between the l890s and the 1990s are those that breed away from lotic and lentic habitats, indicating a severe negative impact from introduced aquatic biota for species that breed in such freshwater situations. On Moloka'i, all damselfly species except one have higher capture rates now than in the l890s, explainable in large part to improved access to previously remote terrain. Among the Carabidae studied, 1990s surveys on Moloka'i have found 12 of 15 species Perkins sampled in the 1890s. Overall, recent surveys have failed to rediscover five species, all of which have been relatively rarely encountered over all decades of the past century. Recent surveys on O'ahu have recollected 17 of the 21 species Perkins found in the 1890s. The most dramatic change in the O'ahu carabid fauna over the past 100 yr is the extinction of the most common O'ahu species of the 1890s, Colpocaccus tantalus (Blackburn). This species was broadly distributed across the island, possessed a well-developed flight apparatus, and accounted for 39% of the specimens captured in the 1890s. It has not been collected since 1940 in spite of intensive collecting during the 1950s and 1990s. The elevational preference of C. tantalus was lower than that for the aggregate balance of the O'ahu carabid fauna, suggesting an altitudinally associated factor in the extinction: most likely ants such as Pheidole megacephala (F.). The loss of a previously dominant generalist species is viewed as an ecological catastrophe, substantially different in quality from extinction of geographically restricted island specialists.
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ItemAdaptive Radiation in the Hawaiian Drosophila (Diptera: Drosophilidae): Ecological and Reproductive Character Analyses(University of Hawaii Press, 1997-10)The entomologist R. C. L. Perkins pioneered observations of breeding site ecology for the endemic Hawaiian Drosophilidae, a renowned group of flies that has undergone explosive speciation and adaptive radiation into a wide variety of breeding niches. Females of the various species groups and subgroups oviposit their eggs in either fungi, flowers, fruits, leaves, stems, bark, sap fluxes, or other novel substrates. Varied selective forces in these alternative breeding sites have apparently molded female reproductive characters and strategies into diverse outcomes; some species mature and oviposit only one egg at a time, whereas others oviposit hundreds. Here, we have analyzed the pattern of shifts in breeding substrate, and the associated evolution of selected ovarian, egg, and ovipositor traits, by mapping the various ecological and female reproductive character states on an independently derived phylogenetic hypothesis based on nuclear and mitochondrial DNA sequences. This comparative phylogenetic approach demonstrates a number of strong historical associations among female reproductive traits and between particular traits and the breeding substrate, although the overall pattern is complex and more data are needed. Identification of certain apomorphic traits associated with shifts in breeding substrate suggests an adaptational origin for some of the changes in egg load per fly, in the length of the respiratory filaments of the egg, and in the length and shape of the ovipositor. Although these hypotheses need further testing, it appears that the ecological diversification in breeding substrates has been an integral component in the radiation of drosophilids in Hawai'i.
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ItemA Hierarchical View of the Hawaiian Drosophilidae (Diptera)(University of Hawaii Press, 1997-10)As the pioneer natural historian of the Hawaiian entomofauna, R. C. L. Perkins showed a keen interest in the Diptera, in general, and the Drosophilidae, in particular. Perkins described and named two of the most charismatic of the Hawaiian picture-winged drosophilid flies: Idiomyia heteroneura and I. silvestris. These two species are part of a chromosomally homosequential quartet of species that have garnered the attention of research programs of numerous biologists. In this paper we review the evidence on the phylogenetic relationships among the flies in this quartet and suggest some guidelines for the inference of phylogeny within this quartet of species as further data accumulate. Perkins was also one of the first to recognize the extent of diversity of the Drosophilidae within and among islands of the archipelago. Several more-recent research programs have concentrated on understanding the evolutionary history of this diversification. Two questions regarding the high degree of diversity of these flies are discussed from a systematic perspective in this paper. The first concerns the relationships of the major species groups assemblages of the Hawaiian drosophilids. The second focuses on the origin of the Hawaiian drosophiloid and scaptomyzoid flies.
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ItemR. C. L. Perkins' Legacy to Evolutionary Research on Hawaiian Drosophilidae (Diptera)(University of Hawaii Press, 1997-10)R. C. L. Perkins' influence on evolutionary research on the Hawaiian Drosophilidae is presented. His observations of the bizarre secondary sexual structures in this group led evolutionary biologists to focus research on the role of sexual selection in speciation and the evolutionary processes responsible for the proliferation of Drosophila species in the native Hawaiian fauna. A review of early taxonomic treatment of the group and some of the ecological novelties of the group are discussed. A better understanding of the genetics, ecology, behavior, morphology, etc. resulted in a revision of the generic concepts of the group, and subsequent phylogenetic studies using modem tools of molecular biology have confirmed the monophyletic relationships among the species in this group.
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ItemHerbivorous Insects and the Hawaiian Silversword Alliance: Coevolution or Cospeciation?(University of Hawaii Press, 1997-10)Numerous groups of herbivorous insects in the Hawaiian archipelago have undergone adaptive radiations. R. C. L. Perkins collected and documented species in nearly all of these groups. In this study I tested whether patterns of host plant use by herbivorous insects can be explained by host plant history. I examined a group of insects in the planthopper genus Nesosydne (Hemiptera: Delphacidae) that feed on plants in the Hawaiian silversword alliance, many of which are endangered or threatened. For these Nesosydne species feeding on the silversword alliance, mitochondrial DNA sequence data revealed a statistically significant pattern of cospeciation between these insects and their hosts. These planthoppers are highly host-specific, with each species feeding on only one, or a few closely related, plant species. Patterns of host plant use across the plant lineage, as well as within extensive hybrid zones between members of the silversword alliance, suggest that planthopper diversification parallels host plant diversification. Data collected thus far are consistent with, but do not directly demonstrate, reciprocal adaptation. For other herbivorous insects associated with members of the Hawaiian silversword alliance, patterns of host plant use and evolutionary history are not yet well understood. However, cospeciation appears not to be universal. For example, endemic flies in the family Tephritidae (Diptera) are less host-specific and demonstrate host-switching. Research is under way to reveal the mechanisms associated with cospeciation and host switching for different insect groups associated with the Hawaiian silversword alliance.
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ItemDispersal and Vicariance in Hawaiian Platynine Carabid Beetles (Coleoptera)(University of Hawaii Press, 1997-10)The monophyletic, native Hawaiian Platynini have diversified on the Hawaiian Island chain through progressive colonization, mixed with vicariance on the various islands. Single-island endemism stands at 97% of the species, with the few widespread species exhibiting distributions largely congruent with the fundamental area cladogram found using cladistic biogeographic methods. The cost of accepting an ad hoc dispersal hypothesis for individual taxa that conflicts with the fundamental area cladogram is weighed against the savings in items of error when taxa are excluded from the biogeographic analysis. Based on this objective assessment, only one back-dispersal from Maui Nui to O'ahu is supported. Vicariance of Maui Nui, leading to the present-day islands of Moloka'i, Lana'i, and Maui, has resulted in seven resolvable species triplets composed of single-island endemics occupying these areas. These seven triplets represent five biogeographic patterns, necessitating explanation by numerous ad hoc hypotheses of extinction to support a single hypothesis of area relationships. In six of the seven triplets, the cladistically basal species exhibits a higher minimum elevational limit of occupied habitat than either of the more apical sister species. This result is consistent with isolation of more persistent, peripheral populations at higher elevations, leading to speciation. Comparison of higher-elevation endemics to lower-elevation widespread species supports this interpretation. Such a finding affirms the importance of understanding geographic distribution on a scale appropriate to the action of vicariant mechanisms.
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ItemLarval Characteristics and Generic Placement of Endemic Hawaiian Hemerobiids (Neuroptera)(University of Hawaii Press, 1997-10)The brown lacewings (Neuroptera: Hemerobiidae) have undergone a spectacular radiation on the Hawaiian Archipelago; currently 23 endemic micromine species are recognized, 19 of which were described by Perkins and four by Zimmerman. Recent systematics studies, using adult morphological characteristics, placed these lacewings in the cosmopolitan genus Micromus. Two of the Hawaiian species (Micromus vagus [from Hawai'i and Maui] and M. rubrinervis [from Hawai'i)) exhibit larval characteristics indicating a close relationship with Micromus. Both species have more larval traits in common with Micromus than with other hemerobiid genera. However, until larvae from the three other genera in Microminae become available, it is not possible to designate whether any of these larval traits are synapomorphic for Micromus. The results also indicate that phylogenetic analyses of the Hemerobiidae should include all instars and that interspecific comparisons should be made on equivalent semaphoronts.
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ItemPhylogenetic Analysis of the Hawaiian Damselfly Genus Megalagrion (Odonata: Coenagrionidae): Implications for Biogeography, Ecology, and Conservation Biology(University of Hawaii Press, 1997-10)A phylogeny of the 22 species currently recognized in the genus Megalagrion, endemic to the Hawaiian Islands, is presented based on an analysis of 23 morphological and ecological characters. After the exclusion ofM. williamsoni, known from only a single male, and inclusion of subspecies within their nominate taxa, a single resolved tree of length 85 was obtained; this tree has a consistency index of 0.56 and a retention index of 0.72. Based on this phylogeny, it appears that the major clades within Megalagrion differentiated on Kaua'i or an antecedent high island. These clades subsequently colonized the younger islands in the chain in an independent and sequential fashion. The phylogeny also implies an ecological progression from ancestral breeding sites in ponds or slow stream pools to breeding on seeps, with the latter habitat having given rise on one hand to a clade of species breeding in phytotelmata or terrestrially, and on the other hand to a clade breeding in rushing midstream waters. The latter ecological progression also indicates a transformation series in larval gill structure from foliate to saccate and eventually to lanceolate. Most species of current conservation concern are shown to be clustered in particular clades, indicating an inherent phylogenetic vulnerability of certain taxon clusters to novel ecological perturbations; the additional species at risk not present in the above clades are endemics confined to the island of O'ahu and have declined because of their geographic provenance.
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ItemPhylogenetic Relationships and Adaptive Shifts among Major Clades of Tetragnatha Spiders (Araneae: Tetragnathidae) in Hawai'i(University of Hawaii Press, 1997-10)The role of adaptive shifts in species formation has been the subject of considerable controversy for many years. Here we examine the phylogeny of a large radiation of Hawaiian spiders in the genus Tetragnatha to determine the extent to which species splitting is associated with shifts in ecological affinity. We use molecular data from ribosomal 12S and cytochrome oxidase mitochondrial DNA, and allozymes to assess phylogenetic affinity. Ecological associations were recorded for all species under study, and shifts are considered in the context of the phylogeny. Results indicate that there are two major clades of Hawaiian Tetragnatha, one of which has abandoned web building (spiny-leg clade), while the other retains the ancestral condition of web building. Within the spiny-leg clade, the molecular information suggests that the species on anyone island are generally most closely related to each other. Preliminary results for the web-building "complex" of species indicate that there may be groups of web builders that have speciated in a similar manner. Results of the study suggest that, at least within the spiny-leg clade, matching sets of taxa have evolved independently on the different Hawaiian islands. There appears to have been a one-to-one convergence of the same set of "ecomorph" types on each island in a manner similar to that of lizards of the Caribbean.